1. Need
In X-ray science it is frequently necessary to reduce the dimensions of a beam of X-rays to a particular optimal size dictated by the experiment.
2. Prior Art
This is often achieved by inserting an adjustable aperture into the beam that consists of moveable “slit blades” made of a dense material which absorbs, or deflect, the unwanted X-rays allowing only the remaining tightly defined beam of the required dimensions to pass through. In many cases (e.g., protein crystallography) where the goal is to achieve a tightly focused X-ray spot with dimensions (which in the ideal case) are closely matched to that of the sample being studied, this slit assembly must be positioned as close as possible to the sample if optimal performance is to be achieved. However, in the immediate vicinity of the sample the available space is extremely limited because many other experimental systems are also clustered tightly around the core experimental area. Hence there is significant demand for a beam defining slit system that is as compact as possible in all three dimensions.
Three prior art approaches are typically used to tackle this problem.
Interchangeable Fixed Apertures
A prior art interchangeable fixed apertures does not allow for the aperture size itself is to be adjustable but instead provides a range of different fixed sized “pinholes” that may be interchanged by a motor drive or installed manually by the experimenter. This is the most compact solution but only a limited number of discrete sizes are available and each one may require re-alignment by skilled staff after installation.
XY Slits
Prior art XY slits typically consist of 4 electric motor driven blades arranged in a “+” shape with above and below blades 110 which are above and below abeam 140 and left and right blades 120 that are to the left and right of beam 140, and that are all approximately perpendicular to beam 140, as shown in prior art FIG. 1. Because all the mechanical and motor systems 130 are perpendicular to the axis of beam 140, the whole assembly may typically be several inches wide and take up a considerable amount of valuable space. The blade pairs 110 and 120 are also typically arranged one-behind-the-other so that the rear pair 120 may be a greater distance from the sample than is optimal. The system may also be mechanically complex with motors, encoders, and gears 130.
XX slits Mounted at the Tips of Extended Lever Arms
Prior art XY slits mounted at the tips of extended lever arms has slit blades mounted on the end of long thin lever arms forming an extended “snout” and are then driven through a mechanical linkage by electric motors set back from the aperture. This allows the parts of the assembly that immediately abut the sample area to be kept more compact, but at the expense of introducing a mechanical linkage system that increases the size of the assembly as a whole, adds additional complexity, and reduces the ultimate accuracy.
Therefore, a compact high precision adjustable beam defining aperture is needed.